RFR (M): 8184334: Generalizing Atomic with templates

[Aleksey Shipilev]

On 07/17/2017 05:49 PM, Erik Österlund wrote:
>> Something like the Unsafe.{get|put|CAS} -Xint performance test would be nice to
>> have.
> 
> Sorry, but I do not understand what you mean here.
> 
> 1) The code only boils down to performing casts that do not change any bit
> pattern, and is by contract forced to be expanded and inlined at compile time,
> so I would be very surprised about any regressions.
> 2) This code executes when we are about to perform atomic operations, so any
> accidental code generated for the casting (which seems odd in the first place),
> I would be very surprised to see.
> 3) Even if there was some barely noticeable regression in fastdebug atomics for
> whatever reason, I do not know if I think it makes sense to pollute the code
> with ugly hacks to micro optimize fastdebug execution time.

I agree that fastdebug should not be our primary optimization target. I was
wondering if all the template magic actually works well in fastdebug builds.

Or product builds, for that matter: because while templates are indeed done
during compile-time, say, the inliner that has to deal with new code shapes can
have opinions.

There are some VarHandles perf tests I have lying around, I can check this
myself today.

-Aleksey